Cycle computer for 16-inch wheels?

[CopperBrompton]

I want to fit a cycle computer to my Brompton, as part of a mileage goal for next year. But most seem to start their wheel diameter range at 18-inch wheels.

Can anyone recommend a cycle computer that works for a Brompton? Preferably wireless as I'm not sure how wires would cope given the bike is typically folded three or four times per day.

 

[deptfordmarmoset]

Most computers allow you to enter the circumference (one revolution) in mm, or diameter x 3.14 anyway. An old handbook for a Sigma 906 gives a ready calculated 1272 for 16''x1.75x2 so the number won't be far off that.

 

[TheDoctor]

I use a cheap Bell one from Asda - seems to work fine.
The calibration number (as above) is the rolling diameter of the wheel.
For a Brommie, (349+width of tyre*2) times pi will be within a few per cent. This assumes that the tyre is as high as it is wide, which is close enough.

 

[CopperBrompton]

Oh, ok, so it's not that they won't work on smaller wheels, just that they haven't included data for them?

 

[TheDoctor]

Exactly so. All a computer does is count how many times the wheel goes round. You could fit one to either wheel of a penny farthing and it would work, as long as you tell it how big the wheel is.
On a Brommie, I would try and get the sensor (the bit on the forks) and the actual computer as close together as possible. It's a long old stem on there. It will all work, though mine tends to get knocked when I fold it. I just have to remember to check that the sensor is close enough to the magnet, or it doesn't read.

 

[CopperBrompton]

Cool. I could even mount the computer lower down - I don't need to read it while cycling, I have the GPS fitted for longer rides, it's just to give me a total mileage year-to-date.

 

[SatNavSaysStraightOn]

I want to fit a cycle computer to my Brompton, as part of a mileage goal for next year. But most seem to start their wheel diameter range at 18-inch wheels...

Cateye include this in their standard information for my micro wireless which gives 2 size for 16" tyres...
but you can just measure out the distance your wheel goes (use 10 rotations with you on the bike for more accuracy) and enter the details manually - would expect something around the 1185-1195 mark...

 

[CopperBrompton]

Thanks, will do the measurement thing.

 

[ufkacbln]

Cool. I could even mount the computer lower down - I don't need to read it while cycling, I have the GPS fitted for longer rides, it's just to give me a total mileage year-to-date.

Why not use the GPS that you use for longer rides.?

A GPS will give you a lot more information than a cycle computer and is easily downloadable into any of the free programmes... enabling a record that can be used to plan, monitor and review

 

[CopperBrompton]

For the Brompton especially, I like the freedom of just 'get on and go' cycling. There's no way I'm going to bother to put the GPS on just to go to the shops.

 

[Brommyboy]

I use an Echo 7 on my Brommy, which has been super-ceded by the Beta. This will set to a very low value. I do not use a table for the setting as this does not allow for compression. I sat on the cycle and wheeled it for a full turn, measuring the distance, ie circumference of the tyre under compression. For me, this comes out at 1295 mm. With the computer set on this, accuracy is within 1%. Just checking, I see that the Beta has been replaced by other models! See http://www.inmotionproducts.com/Computers-c44.htm for details. As long as the computer can be set to a figure above 1000 mm circumference, then it will do for the Brompton.

 

[deptfordmarmoset]

I use an Echo 7 on my Brommy, which has been super-ceded by the Beta. This will set to a very low value. I do not use a table for the setting as this does not allow for compression. I sat on the cycle and wheeled it for a full turn, measuring the distance, ie circumference of the tyre under compression. For me, this comes out at 1295 mm. With the computer set on this, accuracy is within 1%. Just checking, I see that the Beta has been replaced by other models! See http://www.inmotionproducts.com/Computers-c44.htm for details. As long as the computer can be set to a figure above 1000 mm circumference, then it will do for the Brompton.

Purely out of curiosity, do you know how much difference compression makes? On the basis that the wheel doesn't rotate fully along its circumference, I'd expect it to be smaller but that the difference will be very small.

 

[Brommyboy]

For my 700C x 32 tyre on the tourer, the given circumference is 2155 mm but my measured one is 2110 mm, which represents a 2% difference. It will depend on a combination of your tyre pressure and your weight, as to how much compression there is. The setting for the Brompton given by a table would be about (349+37+37) x 3.142= 1329 mm, or about 2.5% different. I obviously run the front wheel of the Brompton softer than on the touring cycle!